There is a need to maintain security of buildings, storage areas, and other facilities to guard against theft, vandalism and other types of damage. This security can be provided by way of a perimeter intruder detection system which is set to detect an intrusion, and to transmit some type of alarm signal.
Some have tried to use optical fibre based intrusion detection systems that operate on the principle of speckle analysis. A speckle pattern is a random intensity pattern produced by the mutual interference of a set of wavefronts. In one intrusion detection system based on this principle a length of optical fibre is attached along a perimeter fence. Laser light of known frequency is introduced at both ends of the optical fibre. Two-dimensional optodetectors are attached at each end of the optical fibre by way of optical splitters which detect the speckle pattern produced by interference of the laser light. The output of the optodetectors is monitored for changes in their speckle patterns.
If the fence is tampered with, then this causes disturbance of the optical fibre and changes in the speckle pattern. This indicates that the fence may be being tampered with and an alarm signal is generated.
The use of laser light and speckle analysis requires the use of laser light sources and sensitive optodetectors along with equipment to monitor the outputs for changes in the speckle pattern. These components can be complex and are thus costly to implement, configure and maintain. There remains a need for alternative intrusion detection systems.